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- Random access memory (RAM)
- Virtual memory
- RAM disk
Computer MemoryIn computing, memory refers to the physical devices used to store programs (sequences of instructions) or data (e.g. program state information) on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which are fast (i.e. RAM), as a distinction from secondary memory, which are physical devices for program and data storage which are slow to access but offer higher memory capacity. Primary memory stored on secondary memory is called "virtual memory". The term "storage" is often (but not always) used in separate computers of traditional secondary memory such as tape, magnetic disks and optical discs (CD-ROM and DVD-ROM). The term "memory" is often (but not always) associated with addressable semiconductor memory, i.e. integrated circuits consisting ofsilicon-based transistors, used for example as primary memory but also other purposes in computers and other digital electronic devices. There are two main types of semiconductor memory: volatile and non-volatile. Examples of non-volatile memory are flash memory (sometimes used as secondary, sometimes primary computer memory) and ROM/PROM/EPROM/EEPROM memory (used for firmware such as boot programs). Examples of volatile memory areprimary memory (typically dynamic RAM, DRAM), and fast CPU cache memory (typically static RAM, SRAM, which is fast but energy-consuming and offer lower memory capacity per area unit than DRAM) . The semiconductor memory is organized into memory cells or bistable flip-flops, each storing one binary bit (0 or 1). The memory cells are grouped into words of fix word length, for example 1, 2, 4, 8, 16, 32, 64 or 128 bit. Each word can be accessed by a binary address of N bit, making it possible to store 2 raised by Nwords in the memory. This implies that processor registers normally are not considered as memory, since they only store one word and do not include an addressing mechanism. Random access memory (RAM)Random access memory (RAM) is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. 
One can read and over-write data in RAM. Many computer systems have a memory hierarchy consisting of CPU registers, on-die SRAM caches, external caches, DRAM, paging systems, and virtual memory or swap space on a hard drive. This entire pool of memory may be referred to as "RAM" by many developers, even though the various subsystems can have very different access times, violating the original concept behind the random access term in RAM. Even within a hierarchy level such as DRAM, the specific row, column, bank, rank, channel, or interleave organization of the components make the access time variable, although not to the extent that rotating storage media or a tape is variable. The overall goal of using a memory hierarchy is to obtain the higher possible average access performance while minimizing the total cost of the entire memory system (generally, the memory hierarchy follows the access time with the fast CPU registers at the top and the slow hard drive at the bottom). In many modern personal computers, the RAM comes in an easily upgraded form of modules called memory modules or DRAM modules about the size of a few sticks of chewing gum. These can quickly be replaced should they become damaged or when changing needs demand more storage capacity. As suggested above, smaller amounts of RAM (mostly SRAM) are also integrated in theCPU and other ICs on the motherboard, as well as in hard-drives, CD-ROMs, and several other parts of the computer system. In addition to serving as temporary storage and working space for the operating system and applications, RAM is used in numerous other ways. 
Virtual memoryVirtual memory - In computing, virtual memory is a memory management technique developed for multitasking kernels. This technique virtualizes a computer architecture's various forms of computer data storage (such as random-access memory and disk storage), allowing a program to be designed as though there is only one kind of memory, "virtual" memory, which behaves like directly addressable read/write memory (RAM). Virtual memory makes application programming easier by hiding fragmentation of physical memory; by delegating to the kernel the burden of managing the memory hierarchy (eliminating the need for the program to handle overlays explicitly); and, when each process is run in its own dedicated address space, by obviating the need to relocate program code or to access memory with relative addressing. Memory virtualization is a generalization of the concept of virtual memory. Virtual memory is an integral part of a computer architecture; implementations require hardware support, typically in the form of a memory management unit built into the CPU. While not necessary, emulators and virtual machines can employ hardware support to increase performance of their virtual memory implementations.[1] RAM diskRAM disk - A RAM disk or RAM drive is a block of RAM (primary storage or volatile memory) that a computer's software is treating as if the memory were a disk drive (secondary storage). It is sometimes referred to as a "virtual RAM drive" or "software RAM drive" to distinguish it from a "hardware RAM drive" that uses separate hardware containing RAM, which is a type of solid-state drive. Shadow RAM - Sometimes, the contents of a relatively slow ROM chip are copied to read/write memory to allow for shorter access times. The ROM chip is then disabled while the initialized memory locations are switched in on the same block of addresses (often write-protected). This process, sometimes called shadowing, is fairly common in both computers and embedded systems. Directory: forms forms -> Form a-122 File No. Retirement homes act, 2010 application under section 116 of the act forms -> Course overview forms -> Pre-matric scholarship for students belonging to the minority communities forms -> Cutting Greenhouse Gases Global warming forms -> Bowl game blarney: Why Sports Tourism Trumps Logic in the Quest for a true College Football Champion in the United States” Prepared for: Dr. Tom Hinch Reviewed by: Tim Enger 0845772 Due Date: December 10, 2005 Word Count: 6,677 forms -> Steven m. Glassman forms -> Teresa k. Blodgett forms -> Atlanta Falcons Internet Scavenger Hunt forms -> Registration information forms -> Chapter 8 seaman to admiral-21 (sta-21) program Download 7.78 Mb. Share with your friends:
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